Substrates containing a resin as a principal component have been employed as substrate films for a wide range of applications since such substrates readily enhance a variety of characteristics such as dimension accuracy, mechanical strength, heat resistance, transparency, and electrical insulation properties. When applied to, for example, a surface protective film for a flat panel display device, a protective film for a solar cell, and the like, such substrates are each typically employed in such a way that an adherend such as a hard coat layer containing a photocurable resin, a thermosetting resin, a thermoplastic resin and/or the like, as a principal component, is overlaid on a surface of the substrate, for the purpose of improving weather resistance, scuff resistance, and the like.
However, the principal component of the hard coat layer is often low in adhesiveness to the substrate. Therefore, when forming the hard coat layer, it is desired to subject to a surface treatment beforehand the substrate or a resin film that is a substrate-forming material. A procedure of the surface treatment has been known which comprises applying onto a surface of the substrate, etc. an emulsion composition containing, for example, water as a dispersion medium, and a polyester dispersed in the water to form a coating film as an easily adhesive layer (see Japanese Unexamined Patent Application, Publication No. 2015-124291). The above-identified publication describes that the improvement of the adhesiveness between the substrate and the hard coat layer is enabled by forming the coating film as the easily adhesive layer on the surface of the substrate, etc. and then forming the hard coat layer on this coating film.
However, due to containing a non-cross-linked resin as a principal component and having insufficient film compactness, the coating film formed from the emulsion composition is likely to permit a component having a relatively low molecular weight (relatively low molecular component) such as an oligomer and an additive contained in the substrate to permeate. Therefore, a laminate in which the substrate and the hard coat layer are laminated with the interposition of the coating film may be accompanied by permeation of the relatively low molecular component through the coating film during use and in turn bleeding out to an interface between the hard coat layer and the coating film, thereby leading to a decrease in adhesiveness between the substrate and the hard coat layer and to a deterioration of appearance thereof.